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          <th colspan="3" align="center">Cursor operations</th>
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          <td width="20%" align="left"><a accesskey="p" href="am_foreign.html">Prev</a> </td>
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    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="am_cursor"></a>Cursor operations</h2>
          </div>
        </div>
      </div>
      <div class="toc">
        <dl>
          <dt>
            <span class="sect2">
              <a href="am_cursor.html#am_curget">Retrieving records with a
        cursor</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="am_cursor.html#am_curput">Storing records with a cursor</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="am_cursor.html#am_curdel">Deleting records with a cursor</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="am_cursor.html#am_curdup">Duplicating a cursor</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="am_cursor.html#am_join">Equality Join</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="am_cursor.html#am_count">Data item count</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="am_cursor.html#am_curclose">Cursor close</a>
            </span>
          </dt>
        </dl>
      </div>
      <p> 
        A database cursor refers to a single key/data pair in the
        database. It supports traversal of the database and is the
        only way to access individual duplicate data items. Cursors
        are used for operating on collections of records, for
        iterating over a database, and for saving handles to
        individual records, so that they can be modified after they
        have been read. 
    </p>
      <p>
        The <a href="../api_reference/C/dbcursor.html" class="olink">DB-&gt;cursor()</a> method opens a cursor into a database. Upon
        return the cursor is uninitialized, cursor positioning occurs
        as part of the first cursor operation. 
    </p>
      <p>
        Once a database cursor has been opened, records may be
        retrieved (<a href="../api_reference/C/dbcget.html" class="olink">DBC-&gt;get()</a>), stored (<a href="../api_reference/C/dbcput.html" class="olink">DBC-&gt;put()</a>), and deleted
        (<a href="../api_reference/C/dbcdel.html" class="olink">DBC-&gt;del()</a>).
    </p>
      <p> 
        Additional operations supported by the cursor handle
        include duplication (<a href="../api_reference/C/dbcdup.html" class="olink">DBC-&gt;dup()</a>), equality join (<a href="../api_reference/C/dbjoin.html" class="olink">DB-&gt;join()</a>), and
        a count of duplicate data items (<a href="../api_reference/C/dbccount.html" class="olink">DBC-&gt;count()</a>). Cursors are
        eventually closed using <a href="../api_reference/C/dbcclose.html" class="olink">DBC-&gt;close()</a>.
    </p>
      <p>
        For more information on the operations supported by the
        cursor handle, see the <a href="../api_reference/C/dbc.html#dbclist" class="olink">Database Cursors and Related
        Methods</a> section in the
        <em class="citetitle">Berkeley DB C API Reference Guide.</em>
    </p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="am_curget"></a>Retrieving records with a
        cursor</h3>
            </div>
          </div>
        </div>
        <p>
        The <a href="../api_reference/C/dbcget.html" class="olink">DBC-&gt;get()</a> method retrieves records from the database
        using a cursor. The <a href="../api_reference/C/dbcget.html" class="olink">DBC-&gt;get()</a> method takes a flag which
        controls how the cursor is positioned within the database and
        returns the key/data item associated with that positioning.
        Similar to <a href="../api_reference/C/dbget.html" class="olink">DB-&gt;get()</a>, <a href="../api_reference/C/dbcget.html" class="olink">DBC-&gt;get()</a> may also take a supplied key and
        retrieve the data associated with that key from the database.
        There are several flags that you can set to customize
        retrieval. 
    </p>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm140526456133072"></a>Cursor position flags</h4>
              </div>
            </div>
          </div>
          <div class="variablelist">
            <dl>
              <dt>
                <span class="term"><a href="../api_reference/C/dbcget.html#dbcget_DB_FIRST" class="olink">DB_FIRST</a>, <a href="../api_reference/C/dbcget.html#dbcget_DB_LAST" class="olink">DB_LAST</a></span>
              </dt>
              <dd> 
                    Return the first (last) record in the
                    database. 
                </dd>
              <dt>
                <span class="term"><a href="../api_reference/C/dbcget.html#dbcget_DB_NEXT" class="olink">DB_NEXT</a>, <a href="../api_reference/C/dbcget.html#dbcget_DB_PREV" class="olink">DB_PREV</a></span>
              </dt>
              <dd> 
                    Return the next (previous) record in the
                    database.
                </dd>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_NEXT_DUP" class="olink">DB_NEXT_DUP</a>
                </span>
              </dt>
              <dd> 
                    Return the next record in the database, if
                    it is a duplicate data item for the current key.
                    For Heap databases, this flag always results in
                    the cursor returning the
                    <code class="literal">DB_NOTFOUND</code> error.
                </dd>
              <dt>
                <span class="term"><a href="../api_reference/C/dbcget.html#dbcget_DB_NEXT_NODUP" class="olink">DB_NEXT_NODUP</a>, <a href="../api_reference/C/dbcget.html#dbcget_DB_PREV_NODUP" class="olink">DB_PREV_NODUP</a></span>
              </dt>
              <dd>
                    Return the next (previous) record in the
                    database that is not a duplicate data item for the
                    current key.
                </dd>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_CURRENT" class="olink">DB_CURRENT</a>
                </span>
              </dt>
              <dd> 
                    Return the record from the database to
                    which the cursor currently refers.
                </dd>
            </dl>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm140526456122336"></a>Retrieving specific key/data pairs</h4>
              </div>
            </div>
          </div>
          <div class="variablelist">
            <dl>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_SET" class="olink">DB_SET</a>
                </span>
              </dt>
              <dd>
                    Return the record from the database that
                    matches the supplied key. In the case of
                    duplicates the first duplicate is returned and the
                    cursor is positioned at the beginning of the
                    duplicate list. The user can then traverse the
                    duplicate entries for the key. 
                </dd>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_SET_RANGE" class="olink">DB_SET_RANGE</a>
                </span>
              </dt>
              <dd>
                    Return the smallest record in the database
                    greater than or equal to the supplied key. This
                    functionality permits partial key matches and
                    range searches in the Btree access method.
                </dd>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_GET_BOTH" class="olink">DB_GET_BOTH</a>
                </span>
              </dt>
              <dd> 
                    Return the record from the database that
                    matches both the supplied key and data items. This
                    is particularly useful when there are large
                    numbers of duplicate records for a key, as it
                    allows the cursor to easily be positioned at the
                    correct place for traversal of some part of a
                    large set of duplicate records. 
                </dd>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_GET_BOTH_RANGE" class="olink">DB_GET_BOTH_RANGE</a>
                </span>
              </dt>
              <dd>
                    If used on a database configured for sorted
                    duplicates, this returns the smallest record in
                    the database greater than or equal to the supplied
                    key and data items. If used on a database that is
                    <span class="emphasis"><em>not</em></span> configured for sorted
                    duplicates, this flag behaves identically to
                    <code class="literal">DB_GET_BOTH</code>.
                </dd>
            </dl>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm140526456140992"></a>Retrieving based on record numbers</h4>
              </div>
            </div>
          </div>
          <div class="variablelist">
            <dl>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_SET_RECNO" class="olink">DB_SET_RECNO</a>
                </span>
              </dt>
              <dd>
                    If the underlying database is a Btree, and
                    was configured so that it is possible to search it
                    by logical record number, retrieve a specific
                    record based on a record number argument.
                </dd>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_GET_RECNO" class="olink">DB_GET_RECNO</a>
                </span>
              </dt>
              <dd> 
                    If the underlying database is a Btree, and
                    was configured so that it is possible to search it
                    by logical record number, return the record number
                    for the record to which the cursor refers.
                </dd>
            </dl>
          </div>
        </div>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm140526456124000"></a>Special-purpose flags</h4>
              </div>
            </div>
          </div>
          <div class="variablelist">
            <dl>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbget.html#dbget_DB_CONSUME" class="olink">DB_CONSUME</a>
                </span>
              </dt>
              <dd> 
                    Read-and-delete: the first record (the
                    head) of the queue is returned and deleted. The
                    underlying database must be a Queue.
                </dd>
              <dt>
                <span class="term">
                  <a href="../api_reference/C/dbcget.html#dbcget_DB_RMW" class="olink">DB_RMW</a>
                </span>
              </dt>
              <dd>
                    Read-modify-write: acquire write locks
                    instead of read locks during retrieval. This can
                    enhance performance in threaded applications by
                    reducing the chance of deadlock.
                </dd>
            </dl>
          </div>
          <p> 
            In all cases, the cursor is repositioned by a <a href="../api_reference/C/dbcget.html" class="olink">DBC-&gt;get()</a>
            operation to point to the newly-returned key/data pair in
            the database.
        </p>
          <p>
            The following is a code example showing a cursor
            walking through a database and displaying the records it
            contains to the standard output:
        </p>
          <a id="prog_am19"></a>
          <pre class="programlisting">int
display(char *database)
    
{
    DB *dbp;
    DBC *dbcp;
    DBT key, data;
    int close_db, close_dbc, ret;

    close_db = close_dbc = 0;

    /* Open the database. */
    if ((ret = db_create(&amp;dbp, NULL, 0)) != 0) {
        fprintf(stderr,
            "%s: db_create: %s\n", progname, db_strerror(ret));
        return (1);
    }
    close_db = 1;

    /* Turn on additional error output. */
    dbp-&gt;set_errfile(dbp, stderr);
    dbp-&gt;set_errpfx(dbp, progname);

    /* Open the database. */
    if ((ret = dbp-&gt;open(dbp, NULL, database, NULL, 
            DB_UNKNOWN, DB_RDONLY, 0)) != 0) {
        dbp-&gt;err(dbp, ret, "%s: DB-&gt;open", database);
        goto err;
    }

    /* Acquire a cursor for the database. */
    if ((ret = dbp-&gt;cursor(dbp, NULL, &amp;dbcp, 0)) != 0) {
        dbp-&gt;err(dbp, ret, "DB-&gt;cursor");
        goto err;
    }
    close_dbc = 1;

    /* Initialize the key/data return pair. */
    memset(&amp;key, 0, sizeof(key));
    memset(&amp;data, 0, sizeof(data));

    /* Walk through the database and print out the key/data pairs. */
    while ((ret = dbcp-&gt;get(dbcp, &amp;key, &amp;data, DB_NEXT)) == 0)
        printf("%.*s : %.*s\n",
            (int)key.size, (char *)key.data,
            (int)data.size, (char *)data.data);
    if (ret != DB_NOTFOUND) {
        dbp-&gt;err(dbp, ret, "DBcursor-&gt;get");
        goto err;
    }

err:    if (close_dbc &amp;&amp; (ret = dbcp-&gt;close(dbcp)) != 0)
        dbp-&gt;err(dbp, ret, "DBcursor-&gt;close");
    if (close_db &amp;&amp; (ret = dbp-&gt;close(dbp, 0)) != 0)
        fprintf(stderr,
            "%s: DB-&gt;close: %s\n", progname, db_strerror(ret));
    return (0);
}</pre>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="am_curput"></a>Storing records with a cursor</h3>
            </div>
          </div>
        </div>
        <p>
        The <a href="../api_reference/C/dbcput.html" class="olink">DBC-&gt;put()</a> method stores records into the database using
        a cursor. In general, <a href="../api_reference/C/dbcput.html" class="olink">DBC-&gt;put()</a> takes a key and inserts the
        associated data into the database, at a location controlled by
        a specified flag.
    </p>
        <p>
        There are several flags that you can set to customize
        storage:
    </p>
        <div class="variablelist">
          <dl>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbcput.html#dbcput_DB_AFTER" class="olink">DB_AFTER</a>
              </span>
            </dt>
            <dd> 
                Create a new record, immediately after the
                record to which the cursor refers. 
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbcput.html#dbcput_DB_BEFORE" class="olink">DB_BEFORE</a>
              </span>
            </dt>
            <dd> 
                Create a new record, immediately before the
                record to which the cursor refers.
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbcget.html#dbcget_DB_CURRENT" class="olink">DB_CURRENT</a>
              </span>
            </dt>
            <dd>
                Replace the data part of the record to which
                the cursor refers. 
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbcput.html#dbcput_DB_KEYFIRST" class="olink">DB_KEYFIRST</a>
              </span>
            </dt>
            <dd> 
                Create a new record as the first of the
                duplicate records for the supplied key. 
            </dd>
            <dt>
              <span class="term">
                <a href="../api_reference/C/dbcput.html#dbcput_DB_KEYLAST" class="olink">DB_KEYLAST</a>
              </span>
            </dt>
            <dd>
                Create a new record, as the last of the
                duplicate records for the supplied key. 
            </dd>
          </dl>
        </div>
        <p> 
        In all cases, the cursor is repositioned by a <a href="../api_reference/C/dbcput.html" class="olink">DBC-&gt;put()</a>
        operation to point to the newly inserted key/data pair in the
        database. 
    </p>
        <p> 
        The following is a code example showing a cursor storing
        two data items in a database that supports duplicate data
        items: 
    </p>
        <a id="prog_am20"></a>
        <pre class="programlisting">int
store(DB *dbp)
    
{
    DBC *dbcp;
    DBT key, data;
    int ret;

    /*
     * The DB handle for a Btree database supporting duplicate data
     * items is the argument; acquire a cursor for the database.
     */
    if ((ret = dbp-&gt;cursor(dbp, NULL, &amp;dbcp, 0)) != 0) {
        dbp-&gt;err(dbp, ret, "DB-&gt;cursor");
        goto err;
    }

    /* Initialize the key. */
    memset(&amp;key, 0, sizeof(key));
    key.data = "new key";
    key.size = strlen(key.data) + 1;

    /* Initialize the data to be the first of two duplicate records. */
    memset(&amp;data, 0, sizeof(data));
    data.data = "new key's data: entry #1";
    data.size = strlen(data.data) + 1;

    /* Store the first of the two duplicate records. */
    if ((ret = dbcp-&gt;put(dbcp, &amp;key, &amp;data, DB_KEYFIRST)) != 0)
        dbp-&gt;err(dbp, ret, "DB-&gt;cursor");

    /* Initialize the data to be the second of two duplicate records. */
    data.data = "new key's data: entry #2";
    data.size = strlen(data.data) + 1;

    /*
     * Store the second of the two duplicate records.  No duplicate
     * record sort function has been specified, so we explicitly
     * store the record as the last of the duplicate set.
     */
    if ((ret = dbcp-&gt;put(dbcp, &amp;key, &amp;data, DB_KEYLAST)) != 0)
        dbp-&gt;err(dbp, ret, "DB-&gt;cursor");

err:    if ((ret = dbcp-&gt;close(dbcp)) != 0)
        dbp-&gt;err(dbp, ret, "DBcursor-&gt;close");

    return (0);
}</pre>
        <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
          <h3 class="title">Note</h3>
          <p>
            If you are using the Heap access method and you are
            creating a new record in the database, then the key that
            you provide to the <a href="../api_reference/C/dbcput.html" class="olink">DBC-&gt;put()</a> method should be empty. The
            <a href="../api_reference/C/dbcput.html" class="olink">DBC-&gt;put()</a> method will return the record's ID (RID) in the
            key. The RID is automatically created for you when Heap
            database records are created. 
        </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="am_curdel"></a>Deleting records with a cursor</h3>
            </div>
          </div>
        </div>
        <p>
        The <a href="../api_reference/C/dbcdel.html" class="olink">DBC-&gt;del()</a> method deletes records from the database using
        a cursor. The <a href="../api_reference/C/dbcdel.html" class="olink">DBC-&gt;del()</a> method deletes the record to which the
        cursor currently refers. In all cases, the cursor position is
        unchanged after a delete.
    </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="am_curdup"></a>Duplicating a cursor</h3>
            </div>
          </div>
        </div>
        <p>
        Once a cursor has been initialized (for example, by a call
        to <a href="../api_reference/C/dbcget.html" class="olink">DBC-&gt;get()</a>), it can be thought of as identifying a particular
        location in a database. The <a href="../api_reference/C/dbcdup.html" class="olink">DBC-&gt;dup()</a> method permits an
        application to create a new cursor that has the same locking
        and transactional information as the cursor from which it is
        copied, and which optionally refers to the same position in
        the database.
    </p>
        <p>
        In order to maintain a cursor position when an application
        is using locking, locks are maintained on behalf of the cursor
        until the cursor is closed. In cases when an application is
        using locking without transactions, cursor duplication is
        often required to avoid self-deadlocks. For further details,
        refer to <a class="xref" href="lock_am_conv.html" title="Berkeley DB Transactional Data Store locking conventions">Berkeley DB Transactional Data
        Store locking conventions</a>.
    </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="am_join"></a>Equality Join</h3>
            </div>
          </div>
        </div>
        <p>
        Berkeley DB supports "equality" (also known as "natural"),
        joins on secondary indices. An equality join is a method of
        retrieving data from a primary database using criteria stored
        in a set of secondary indices. It requires the data be
        organized as a primary database which contains the primary key
        and primary data field, and a set of secondary indices. Each
        of the secondary indices is indexed by a different secondary
        key, and, for each key in a secondary index, there is a set of
        duplicate data items that match the primary keys in the
        primary database.
    </p>
        <p>
        For example, let's assume the need for an application that
        will return the names of stores in which one can buy fruit of
        a given color. We would first construct a primary database
        that lists types of fruit as the key item, and the store where
        you can buy them as the data item:
    </p>
        <div class="informaltable">
          <table border="1" width="80%">
            <colgroup>
              <col />
              <col />
            </colgroup>
            <thead>
              <tr>
                <th>Primary key:</th>
                <th>Primary data:</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td align="left">apple</td>
                <td align="left">Convenience Store</td>
              </tr>
              <tr>
                <td align="left">blueberry</td>
                <td align="left">Farmer's Market</td>
              </tr>
              <tr>
                <td align="left">peach</td>
                <td align="left">Shopway</td>
              </tr>
              <tr>
                <td align="left">pear</td>
                <td align="left">Farmer's Market</td>
              </tr>
              <tr>
                <td align="left">raspberry</td>
                <td align="left">Shopway</td>
              </tr>
              <tr>
                <td align="left">strawberry</td>
                <td align="left">Farmer's Market</td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
        We would then create a secondary index with the key
        <span class="bold"><strong>color</strong></span>, and, as the data
        items, the names of fruits of different colors.
    </p>
        <div class="informaltable">
          <table border="1" width="80%">
            <colgroup>
              <col />
              <col />
            </colgroup>
            <thead>
              <tr>
                <th>Secondary key:</th>
                <th>Secondary data:</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td align="left">blue</td>
                <td align="left">blueberry</td>
              </tr>
              <tr>
                <td align="left">red</td>
                <td align="left">apple</td>
              </tr>
              <tr>
                <td align="left">red</td>
                <td align="left">raspberry</td>
              </tr>
              <tr>
                <td align="left">red</td>
                <td align="left">strawberry</td>
              </tr>
              <tr>
                <td align="left">yellow</td>
                <td align="left">peach</td>
              </tr>
              <tr>
                <td align="left">yellow</td>
                <td align="left">pear</td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
        This secondary index would allow an application to look up a
        color, and then use the data items to look up the stores where
        the colored fruit could be purchased. For example, by first
        looking up <span class="bold"><strong>blue</strong></span>, the data
        item <span class="bold"><strong>blueberry</strong></span> could be used
        as the lookup key in the primary database, returning <span class="bold"><strong>Farmer's Market</strong></span>.
    </p>
        <p>
        Your data must be organized in the following manner in order
        to use the <a href="../api_reference/C/dbjoin.html" class="olink">DB-&gt;join()</a> method:
    </p>
        <div class="orderedlist">
          <ol type="1">
            <li>
            The actual data should be stored in the database
            represented by the <a href="../api_reference/C/db.html" class="olink">DB</a> object used to invoke this method.
            Generally, this <a href="../api_reference/C/db.html" class="olink">DB</a> object is called the
            <span class="emphasis"><em>primary</em></span>.
        </li>
            <li>
            Secondary indices should be stored in separate
            databases, whose keys are the values of the secondary
            indices and whose data items are the primary keys
            corresponding to the records having the designated
            secondary key value. It is acceptable (and expected) that
            there may be duplicate entries in the secondary indices.
                <p>
                    These duplicate entries should be sorted for
                    performance reasons, although it is not required. For
                    more information see the <a href="../api_reference/C/dbset_flags.html#dbset_flags_DB_DUPSORT" class="olink">DB_DUPSORT</a> flag to the
                    <a href="../api_reference/C/dbset_flags.html" class="olink">DB-&gt;set_flags()</a> method.
                </p></li>
          </ol>
        </div>
        <p>
        What the <a href="../api_reference/C/dbjoin.html" class="olink">DB-&gt;join()</a> method does is review a list of secondary
        keys, and, when it finds a data item that appears as a data
        item for all of the secondary keys, it uses that data item as
        a lookup into the primary database, and returns the associated
        data item.
    </p>
        <p>
        If there were another secondary index that had as its key
        the <span class="bold"><strong>cost</strong></span> of the fruit, a
        similar lookup could be done on stores where inexpensive fruit
        could be purchased:
    </p>
        <div class="informaltable">
          <table border="1" width="80%">
            <colgroup>
              <col />
              <col />
            </colgroup>
            <thead>
              <tr>
                <th>Secondary key:</th>
                <th>Secondary data:</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td align="left">expensive</td>
                <td align="left">blueberry</td>
              </tr>
              <tr>
                <td align="left">expensive</td>
                <td align="left">peach</td>
              </tr>
              <tr>
                <td align="left">expensive</td>
                <td align="left">pear</td>
              </tr>
              <tr>
                <td align="left">expensive</td>
                <td align="left">strawberry</td>
              </tr>
              <tr>
                <td align="left">inexpensive</td>
                <td align="left">apple</td>
              </tr>
              <tr>
                <td align="left">inexpensive</td>
                <td align="left">pear</td>
              </tr>
              <tr>
                <td align="left">inexpensive</td>
                <td align="left">raspberry</td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
        The <a href="../api_reference/C/dbjoin.html" class="olink">DB-&gt;join()</a> method provides equality join functionality.
        While not strictly cursor functionality, in that it is not a
        method off a cursor handle, it is more closely related to the
        cursor operations than to the standard <a href="../api_reference/C/db.html" class="olink">DB</a> operations.
    </p>
        <p>
        It is also possible to do lookups based on multiple criteria
        in a single operation. For example, it is possible to look up
        fruits that are both red and expensive in a single operation.
        If the same fruit appeared as a data item in both the color
        and expense indices, then that fruit name would be used as the
        key for retrieval from the primary index, and would then
        return the store where expensive, red fruit could be
        purchased.
    </p>
        <div class="sect3" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h4 class="title"><a id="idm140526456046816"></a>Example</h4>
              </div>
            </div>
          </div>
          <p>
            Consider the following three databases:
        </p>
          <div class="variablelist">
            <dl>
              <dt>
                <span class="term">personnel</span>
              </dt>
              <dd>
                <div class="itemizedlist">
                  <ul type="disc">
                    <li>key = SSN</li>
                    <li>data = record containing name,
                            address, phone number, job
                            title</li>
                  </ul>
                </div>
              </dd>
              <dt>
                <span class="term">lastname</span>
              </dt>
              <dd>
                <div class="itemizedlist">
                  <ul type="disc">
                    <li>key = lastname</li>
                    <li>data = SSN</li>
                  </ul>
                </div>
              </dd>
              <dt>
                <span class="term">jobs</span>
              </dt>
              <dd>
                <div class="itemizedlist">
                  <ul type="disc">
                    <li>key = job title</li>
                    <li>data = SSN</li>
                  </ul>
                </div>
              </dd>
            </dl>
          </div>
          <p>
            Consider the following query:
        </p>
          <pre class="programlisting">Return the personnel records of all people named smith with the job
title manager.</pre>
          <p>
            This query finds are all the records in the primary
            database (personnel) for whom the criteria <span class="bold"><strong>lastname=smith and job
            title=manager</strong></span> is true.
        </p>
          <p>
            Assume that all databases have been properly opened and
            have the handles: pers_db, name_db, job_db. We also assume
            that we have an active transaction to which the handle txn
            refers.
        </p>
          <a id="prog_am21"></a>
          <pre class="programlisting">DBC *name_curs, *job_curs, *join_curs;
DBC *carray[3];
DBT key, data;
int ret, tret;

name_curs = NULL;
job_curs = NULL;
memset(&amp;key, 0, sizeof(key));
memset(&amp;data, 0, sizeof(data));

if ((ret =
    name_db-&gt;cursor(name_db, txn, &amp;name_curs, 0)) != 0)
    goto err;
key.data = "smith";
key.size = sizeof("smith");
if ((ret =
    name_curs-&gt;get(name_curs, &amp;key, &amp;data, DB_SET)) != 0)
    goto err;

if ((ret = job_db-&gt;cursor(job_db, txn, &amp;job_curs, 0)) != 0)
    goto err;
key.data = "manager";
key.size = sizeof("manager");
if ((ret =
    job_curs-&gt;get(job_curs, &amp;key, &amp;data, DB_SET)) != 0)
    goto err;

carray[0] = name_curs;
carray[1] = job_curs;
carray[2] = NULL;

if ((ret =
    pers_db-&gt;join(pers_db, carray, &amp;join_curs, 0)) != 0)
    goto err;
while ((ret =
    join_curs-&gt;get(join_curs, &amp;key, &amp;data, 0)) == 0) {
    /* Process record returned in key/data. */
}

/*
 * If we exited the loop because we ran out of records,
 * then it has completed successfully.
 */
if (ret == DB_NOTFOUND)
    ret = 0;

err:
if (join_curs != NULL &amp;&amp;
    (tret = join_curs-&gt;close(join_curs)) != 0 &amp;&amp; ret == 0)
    ret = tret;
if (name_curs != NULL &amp;&amp;
    (tret = name_curs-&gt;close(name_curs)) != 0 &amp;&amp; ret == 0)
    ret = tret;
if (job_curs != NULL &amp;&amp;
    (tret = job_curs-&gt;close(job_curs)) != 0 &amp;&amp; ret == 0)
    ret = tret;

return (ret);</pre>
          <p>
            The name cursor is positioned at the beginning of the
            duplicate list for <span class="bold"><strong>smith</strong></span>
            and the job cursor is placed at the beginning of the
            duplicate list for <span class="bold"><strong>manager</strong></span>.
            The join cursor is returned from the join method. This code then
            loops over the join cursor getting the personnel records of each one
            until there are no more.
        </p>
        </div>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="am_count"></a>Data item count</h3>
            </div>
          </div>
        </div>
        <p>
        Once a cursor has been initialized to refer to a particular
        key in the database, it can be used to determine the number of
        data items that are stored for any particular key. The
        <a href="../api_reference/C/dbccount.html" class="olink">DBC-&gt;count()</a> method returns this number of data items. The
        returned value is always one, unless the database supports
        duplicate data items, in which case it may be any number of
        items.
    </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="am_curclose"></a>Cursor close</h3>
            </div>
          </div>
        </div>
        <p>
        The <a href="../api_reference/C/dbcclose.html" class="olink">DBC-&gt;close()</a> method closes the <a href="../api_reference/C/dbc.html" class="olink">DBC</a> cursor, after which
        the cursor may no longer be used. Although cursors are
        implicitly closed when the database they point to are closed,
        it is good programming practice to explicitly close cursors.
        In addition, in transactional systems, cursors may not exist
        outside of a transaction and so must be explicitly
        closed.
    </p>
      </div>
    </div>
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